Great attention has been paid to ceramic materials for their heat resistance, wear resistance, high-temperature strength and other advantages. However, ceramic materials are very difficult to mechanically work since they are hard and brittle. Thus most ceramic articles are prepared by sintering and precursor methods. The sintering method involves the step of pressing or otherwise forming a ceramic material in powder form into a desired shape followed by firing. The precursor method is by melting an organic polymer as a ceramic precursor or dissolving it in a suitable solvent, forming the melt or solution into a desired shape, and then firing for converting the polymer into inorganic form. The precursor method is characterized by the potential manufacture of ceramic articles to a configuration which cannot be achieved with the powder sintering method, and especially adapted for the manufacture of fibers.
Among ceramics, SiC and Si.sub.3 N.sub.4 are of great interest for high-temperature performance, more particularly because of heat resistance and high-temperature strength for the former and thermal shock resistance and fracture toughness for the latter. Extensive research works have been made on their precursors.
Most ceramic materials prepared by prior art well-known ceramic precursor methods are of Si-C-O, Si-C-N and Si-C-N-O systems although some ceramics are known to have metals such as Ti and Zr incorporated therein. A typical polymer having such a metal incorporated therein is a polytitanocarbosilane prepared by reaction of polytitanocarbosilane with titanoalkoxide as disclosed in U.S. Pat. No. 4,359,559 or Japanese Patent Application Kokai No. 74126/1981. Firing of polytitanocarbosilane, however, results in a Si-Ti-O-C ceramic system which suggests the presence of much oxygen in the ceramic. These oxygen rich ceramic materials undesirably experience an acute loss of strength at temperatures higher than 1,300.degree. C. due to promoted crystallization.
In turn, U.S. Pat. No. 4,312,970 or Japanese Patent Application Kokai No. 139124/1982 discloses Si-C-N and Si-C-N-O ceramic systems. The present inventors examined the strength and crystallization of these ceramic materials to find that crystallization proceeded at temperatures higher than 1,300.degree. C. resulting in a sudden loss of strength.
Further, the prior art known ceramic precursor methods have forming and working problems and suffer from low production yields.
The present invention is to eliminate the above-mentioned drawbacks of the prior art, and its object is to provide a method for preparing a ceramic precursor having forming and working flexibility and ensuring high ceramic production yields as well as a method for preparing a ceramic material having practical heat resistance at temperatures of higher than 1,300.degree. C. using the ceramic precursor.